Management of Incomitant Deviations Flashcards
What do we need to know from the investigation into incomitant deviations?
Diagnosis
- Paresis (some muscle movement so a -1 to -3 on OMs)
- Paralysis (-4+ on OMs)
Level of Incomitance
- Muscle Sequelae
- Secondary larger than Primary deviation
Differential Diagnosis
- Acquired vs. Congenital
- Recent vs. Longstanding
Symptoms
- Diplopia
- Pain
- Ptosis
- Reduced VA
- Nystagmus
- Other
What symptoms do we need to know about diplopia?
- Constant or Intermittent
- Direction (Horizontal, Vertical or Torsional)
- Largest Separation of Images (in what gaze position, near or distance or both fixation distances)
- Relieve Diplopia by Closing 1 Eye? (Monocular diplopia often comes from cataracts)
What symptoms do we need to know about in incomitant strabismus?
Pain
- When & which position?
Reduced/Loss VA
- Colour vision
- Contrast sensitivity
- Visual field defect
Ptosis
- Complete/Partial
Nystagmus
- Type & direction
- Constant or intermittent
- Oscillopsia (seen in recently acquired strabismus where the world wobbles.
How long should we observe for in incomitant strabismus?
To allow time for spontaneous recovery before surgery you should allow for 9 - 12 months of observation and for ocular motility to be stable for at least 3 months
What 3 methods do we have for reliving or minimising diplopia?
- Teach AHP
- Prisms
- Occlusion
What is the aim of an AHP?
To move the eyes away from the field of action of the paresed muscle and to move the eyes to a position where the deviation is least
What are the aims of prism use in managing incomitant deviations?
- Aim of prisms is to restore prism using the smallest prism amount
- Move the image into suppression area if potential BSV absent
- To further separate the images if there’s no BSV potential or suppression area
What does the type of prism depend upon in managing incomitant deviations?
- Direction of diplopia
- Constant/ intermittent diplopia
- Distance(s) appreciate diplopia
- Position(s) of gaze appreciate diplopia
- Duration and stability of deviation
What options are there for prism use in managing incomitant deviations?
- Temporary – Fresnel prisms
- Permanent – incorporate prisms
How should we fit prisms when using them to manage incomitant deviations?
- Full lens
- Distance or reading glasses only
- Upper segment or bifocal segment
- Split prisms
What are the disadvantages of Fresnel prisms?
- Horizontal magnification
- Vertical magnification
- Curvature of vertical lines (less so in prisms incorporated into glasses)
Asymmetric horizontal magnification - Change in vertical magnification with horizontal angle
- Chromatic Dispersion
- Dynamic Visual Acuity (DVA)
What does ‘Chromatic Dispersion’ lead to?
Part of the disadvantages of Fresnel prisms
- Diffraction of light by grooves in Fresnel prism
- Cause reduced contrast
Effect VA, contrast sensitivity, fusion and stereoacuity
Reduction substantial if prism >10∆ - 10∆ prism (Kulnig, 1987)
Incorporated into glasses: reduce VA to 6/9 (~0.15 logMAR)
Fresnel prisms: reduce VA to 6/12 (0.30 logMAR)
What is ‘Dynamic Visual Acuity’ (DVA)?
- The ability to discriminate an object when there is movement between object and individual
- DVA is increasingly reduced as fresnel prism strength increased
Identification of orientation of a moving Landolt C viewed at 57cm (Maconachie et al. 2010)
What did Knight & Griffiths (2011) find about Fresnel Prisms?
Driving standard require VA between 0.2-0.3 logMAR
In photopic condition using >15 dioptre prism participants should not be driving
In mesopic conditions using >5 dioptres participants should not be driving
What are the advantages of Fresnel prisms?
- Orientation of prism has no effect on VA and contrast sensitivity (Veronneau-Troutman, 1978)
- Lightweight
- Easily changeable
- May relieve AHP
- May allow return to work & ability to do daily tasks
How do we fit Fresnel prisms?
- Draw outline slightly smaller than edge of lens using non-permanent marker pen
- Place under water
- Apply prism to back surface of lens
If very high curvature (high myopic correction) apply to front surface - Remove air bubbles by wiping/pressing in apex to base direction
When should we incorporate prisms?
- Stable angle of deviation (after observation period)
- Comfortable in prisms
Reasonably concomitant - Power of prism relatively small (<8 PD either eye)
- Surgery contraindicated
What problems do we have with incorporating prisms?
Weight and edge thickness
How successful are prisms in CNIV palsy?
- Prisms useful if relatively small vertical deviation in P.P. and fairly concomitant
- Full correction of angle often required to relieve diplopia
Exception: longstanding with extended vertical fusion range
What is the exception to using fully correcting prisms in CNIV palsy?
Exception: longstanding with extended vertical fusion range
How successful are prisms for managing CNVI palsy?
- Prisms useful if minimal/small amount of lateral incomitance
- Typical prism prescribed for horizontal deviations is generally 50% of the total deviation
When are prisms most successful for treating incomitant deviations?
- Successful use of prisms more likely if realistic patient expectations
- Frequent follow-up,
- Patient >65 years
What did the Diplopia impacts on patients’ health related quality of life (HRQOL) study from Hatt et al (2014) study?
Hatt et al (2014) performed a retrospective study including 34 patients (aged 14-84 years) with diplopia
Aim: determine if successful treatment of diplopia improve HRQOL
Method: two questionnaires pre-prism treatment and at follow up
- Diplopia questionnaire: rate severity of diplopia (5-point scale)
- Adult strabismus questionnaire: four areas
Self-perception
Reading
Interactions
General function
What did the Diplopia impacts on patients’ health related quality of life (HRQOL) study by Hatt et al (2014) find?
Results: 23 of 34 were successfully treated with prisms
- 74% were prescribed Fresnel prism and 26% had prisms incorporated
- Significant improvement in
1. Diplopia questionnaire
- Adult strabismus 20 questionnaire
Improvement in general and reading function
Unchanged for self-perception and interactions
How is PAT / Diagnostic Occlusion used in CNVI palsy?
Aim: determine the true angle of deviation
Advocated for longstanding unilateral SO palsy
Prism Adaptation
Method:
Fully correct angle of deviation with prisms for 1-2 weeks
Perform PCT on return to determine if angle has increased
Diagnostic occlusion
Method:
Occlude the paretic eye (non-fixing eye) for 1 day - 2 weeks FT.
Perform PCT before occlusion and on return without allowing binocular vision
What does Occlusion used in managing incomitant deviations depend on?
- Constant/ intermittent diplopia
- Position(s) of gaze appreciate diplopia
- Duration and stability of deviation
What are the options of occlusion?
- Blenderm
- Bangerter Foils
- Frosted Lens
- Occlusive Contact Lens
How can we fit occlusion options?
- Total occlusion
- Lower or upper segment occlusion
- Sector occlusion (primarily used in 4th nerves)
What outcomes could there be after the observation period in managing incomitant deviations?
- Recovered
- Stable
- Deteriorated
What ocular factors affect the management of incomitant deviations?
- Severity of symptoms
- Duration since onset
- Presence and size of AHP
- Binocular functions
- Torsion
- Appearance
